10.1021/ja020411a.s001
Brian S. J. Blagg
Brian
S. J. Blagg
Michael B. Jarstfer
Michael B.
Jarstfer
Daniel H. Rogers
Daniel H.
Rogers
C. Dale Poulter
C. Dale
Poulter
Recombinant Squalene Synthase. A Mechanism for the
Rearrangement of Presqualene Diphosphate to Squalene
American Chemical Society
2002
HSQ
Recombinant Squalene Synthase
rearrangement
ROH
DSQ
Squalene Squalene synthase
form presqualene diphosphate
presence
NADPH 3
biosynthesi
C 30 analogue
cyclopropylcarbinyl alcohol
SQ
PSPP
stereochemistry
SQase
FPP
2002-07-04 00:00:00
Journal contribution
https://acs.figshare.com/articles/journal_contribution/Recombinant_Squalene_Synthase_A_Mechanism_for_the_Rearrangement_of_Presqualene_Diphosphate_to_Squalene/3640938
Squalene synthase (SQase) catalyzes the condensation of two molecules of farnesyl diphosphate
(<b>FPP</b>) to form presqualene diphosphate (<b>PSPP</b>) and the subsequent rearrangement and NADPH-dependent
reduction of <b>PSPP</b> to squalene (<b>SQ</b>). These reactions are the first committed steps in cholesterol
biosynthesis. When recombinant SQase was incubated with <b>FPP</b> in the presence of dihydroNADPH
(NADPH<sub>3</sub>, an unreactive analogue lacking the 5,6-double bond in the nicotinamide ring), three products
were formed: dehydrosqualene (<b>DSQ</b>), a C<sub>30</sub> analogue of phytoene; 10(<i>S</i>)-hydroxysqualene <b>(HSQ</b>), a
hydroxy analogue of squalene; and rillingol (<b>ROH</b>), a cyclopropylcarbinyl alcohol formed by addition of
water to the tertiary cyclopropylcarbinyl cation previously proposed as an intermediate in the rearrangement
of <b>PSPP</b> to <b>SQ</b> (Poulter, C. D. <i>Acc. Chem. Res</i>. <b>1990</b>, <i>23</i>, 70−77). The structure and absolute
stereochemistry of the tertiary cyclopropylcarbinyl alcohol were established by synthesis using two
independent routes. Isolation of <b>ROH</b> from the enzyme-catalyzed reaction provides strong evidence for a
cyclopropylcarbinyl−cyclopropylcarbinyl rearrangement in the biosynthesis of squalene. By comparing the
SQase-catalyzed solvolysis of <b>PSPP</b> in the absence of NADPH<sub>3</sub> to the reaction in the presence of NADPH<sub>3</sub>,
it is apparent that the binding of the cofactor analogue substantially enhances the ability of SQase to control
the regio- and stereochemistry of the rearrangements of <b>PSPP</b>.